Purpose of HIC

[sujins]

I've just wonder the function of HIC (Hand indicate controller). Is it used to manual open for control valve,etc during startup or shutdown in process or...? In some design, the system have a control valve which can operate in "AUTO" and "Manual" mode why do we need to have HIC to manual open or close that control valve? Please anyone who know the answer give explanation or recommend the related book? Thanks.

 

[bmsg]

What you are referring to as HIC is called an Auto-manual Station or a Manual Loader.

From the configuration you describe, this station (which may be either a panel mounted hardware or a software entity, in your case)will normally allow the control valve to be manipulated (i.e., opened / closed) from the signal of an automatic controller (that executes some kind of an algorithm inside it).

However, should you desire to control the valve manually, i.e., open it or close it or put it in an intermediate position, bypassing the signal from the controller, this is possible from the HIC.

The HIC will have buttons to allow you to select 'Auto' action from the controller or 'Manual' operation from the HIC itself.

I hope I have been able to clarify your query.

 

[Ashereng]

bmsg,

Good explanation.

There is also a HOA (Hand-Off-Auto). When in Hand, the Start/Stop switch local to the motor is in use. When in Off, the motor is off, no power to starter. When in Auto, the PLC/DCS controls.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[JLSeagull]

There are a few good uses for the HIC and some obsolete applications. The DCS options could be a modern approach compared to a pneumatic manual loader.

Perhaps a controller has multiple outputs, like a split range application via a DCS. Some control applications include two valves that work in sequence. One could use 4-12 mA or 3-9 psig to stroke the first valve and 12-20 mA or 9-15 psig to stroke a second valve. Another option is to characterize the outputs from the PID block using two analog outputs. In the case of two outputs the auto/manual stations provide the operator or maintenance technician the ability to manually control either valve instead of the entire loop output.

In an older pneumatic scheme some plants used a manual selector near the valve or other control device where the control room was far from the field equipment. Reasons could be the lack of radio communications during startup, poor reliability etc.

 

[Ashereng]

One could use 4-12 mA or 3-9 psig to stroke the first valve and 12-20 mA or 9-15 psig to stroke a second valve.

Interesting. I have never seen a split range set up like that. Usually, the output of the controller (eg PID) goes to two separate output blocks, such that 0%-60% OP equals 0%-100% (4-20 mA) for one valve and 40%-100% OP equals 0%-100% (4-20 mA) for the second valve. Or some variations thereof.




"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[JLSeagull]

Ya see, you yungins can lern a thing er too from we old guys.

 

[Ashereng]

Okay. Sounds good.

Would you explain the benefits of 4-12mA (3-9 psi) and 12-20mA (9-15 psi)?

For example, how does the actuator work on 9-15 psi?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[JLSeagull]

Let's assume that the valve is stroked by 3-15 psig air. You can calibrate the positioner for 3-9 psig input or a 9-15 psig input to cause a full 3-15 psig output. In this manner one 3-15 psig signal can operate two seperate valves in sequence. The same thing can be done with most 4-20 mA valve transducers to calibrate a 4-20 mA output on a 4-12 mA or 12-20 mA input. There is nothing special about a 50% split as many such devices can use any 1/3rd of the input range to generate the full output range.

Still several advantages exist using multiple DCS outputs. Explore the alternatives when insufficient signal wire exists, etc.

 

[Ashereng]

JL,

Okay. Thanks for the explanation.

I don't think I will use the technique though.

The primary reason is that the positioner is "custom calibrated" to 3-9psi/9-15psi. It is too easy to miss this when replacing the positioner. The instr tech is thinking 3-15psi.

A secondary reason is preference. I prefer to leave the field side as consistent as I can - 3-15psi, 4-20mA. Any split range, I leave in the control system.

Just my $0.02.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?